I removed all internet plugins except AdobePDFViewer.plugin in Library/Internet Plug-Ins and now it work.
Now all I have to do is to find out the conflicting internet plugin, I suspect that the culprit is LogMeIn.plugin or LogMeInSafari32.plugin since those are the newest ones to be installed.
I will get back to this when I found out the conflicting one(s).